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After opening a stem for repair I always put on the Vac pump. Will run it to at least 500 microns before isolating and confirming no leak. If the system was open for installing or replacing a drier than I know a lot more moisture got in. It SEEMS that the pump dowm takes longer to get the moisture out. Question to you techs: When I isolate the pump at 500 microns (got a good "Val-Chek") and it still creeps up, I assume there is still moisture in the system that needs to be boiled off. SO.... I keep the pump running until I am certain I've fully boiled everthing off. EVERYONE else at my company does NOT. They typically pump it down for, say 15-30 minutes and think its good enough. Most don't have a micron gage. They say "time is money" and I'm just wasting time. I wish to be CERTAIN there is NO leak AND got all the air + moisture from the system.
PLEASE give me your feedback and what procedure(s) work for you.

Sounds about like what everyone at our place does. We had some hacks a few years ago that pulled lousy vacuums. The techs kept following them around cleaning up their messes. That costs more than doing it right to begin with.

Don't know if I'm missing something at a poor connection. New JB 5 cfm pump; has a 3-way tee for hoses. Connected new high pressure black charging hose to tee and micron gage. Used new caps on other two hose ports and tested. CAN pull down to 75 microns with pump running. But when I isolate, the micron gage rises past 500. QUESTIONS: If a system still had a leak, would the pump even allow me to pull such a low vac ( again, with pump running)? Does it sound like the caps will not provide a proper seal while checking a vacuum?

One thing you have to remember is that there is a lot of tubing and surface area in a typical a/c unit. When you are pulling down a vacuum you are pulling air from a long distance off.

That said, it does take some time to pull from the farthest spaces of the evap coil to the pump. Having the micron gauge at the pump isn't necessarily telling you what the vacuum level is deep in the system; that's why you must blank off the pump during the evac process. This will let the system equalize and give you a truer system evac level.

Pulling down to 300 microns and holding below 500 for 15 minutes is what I do. A leak shoud keep going towards atmosphere. Water in the system is indicated by a leveling out at approx. 1200 microns.

Pulling down below 250 microns is hard to do because of the permability of gauge hoses. Using copper lines instead of hoses lets you get a deeper vacuum, but it isn't really necessary for a/c systems.

Originally posted by on call Pulling down below 250 microns is hard to do because of the permability of gauge hoses. Using copper lines instead of hoses lets you get a deeper vacuum, but it isn't really necessary for a/c systems.

I bought three stainless steel hoses not long ago and use them for evacuation only.

Someone can correct me if I'm wrong, but I take the same steps and procedures on every system I evacuate no matter what size or type of system. I've read many articles on evacuation and come upon the same thing...moisture hurts systems. I've said it here before and will again...since being on this site and reading literature, I've changed the way I evacuate a system. I feel I perform the process in the best way I know how. Core removal tools, stainless steel hoses, micron attached to the system...not the pump, oil changed every two, or less, evacuations.

If it's overkill on residential systems, I don't care...at least I can take this step out of the loop if there ever is a problem pertaining to the system.

Others may disagree with the evacuation process. Check out these websites and read their articles for more information.

OK, so pulling down to 300 microns and holding below 500 isn't enough for comfort cooling, then what is?

I don't want to labor the point, but I haven't seen anything that says you have to go lower than the 300 microns.

Sure, the more water you get out of the system, the better off the system will be. Getting out the remaining water is the job of the dessicant. Besides, in a POE system, I don't care if you pull the system down to 1 micron, you are still going to have to rely on the dryer to remove the rest of the moisture.

I feel there is a law of diminishing returns when you're down to low micron readings. Yes, get them as low as you reasonably can, but at a certain point system performance won't be impacted. I really question saying that someone pulling a deeper vacuum than 300 microns is necesarrily doing a better install.

BTW ARI 710-86 states that the end-point dryness for R-22 must reach at least 60 PPM using a filter drier.

If I am wrong, I would really like to see some literature stating otherwise.

I never implied that pulling down to 300 microns was the norm for me. In fact, some manufactures say that 1000 microns is good enough. I will pull it down to under 500.

When I'm installing a system that is to be evacuated that day, piping the system in and putting it on a vacuum is the first thing I do. I'll leave it there until the majority of the work is done. I will check it often to make sure it's doing it's job, but I see no harm in leaving a system in a vacuum while monitoring it, even if it's reached under 500 microns.

While we are on the subject I use a 4 hose manifold I hook up the high and low side as normal vacuum hose to vacuum pump and charging hose to micron gauge
Seems like it doesnt matter what system or how long it runs single evac or triple it will not settle and stay at 500 no matter what it always settles in around 900
I have pulled systems down to below 300 and let it sit and when I go back it at 900 ish it will stay in the 900s for ½ hr to 45 min
So I have always figured it was hoses or manifold that would not let it stay any lower have always heard that without using all vacuum hoses it could climb some and settle as long as it stays below 1000 it is ok
Am I missing something??? Should I change what Im doing?